Refining the Formula That Predicts Celebrity Marriages’ Doom

In 2006, Garth Sundem and I confronted one of the great unsolved mysteries in social science: Exactly how soon will a given celebrity marriage blow up?

Drawing on Garth’s statistical expertise and my extensive survey of the literature in supermarket checkout lines, we published an equation in The New York Times predicting the probability that a celebrity marriage would endure. The equation’s variables included the relative fame of the husband and wife, their ages, the length of their courtship, their marital history, and the sex-symbol factor (determined by looking at the woman’s first five Google hits and counting how many show her in skimpy attire, or no attire).

Now, with more five years of follow-up data, we can report firm empirical support for the Sundem/Tierney Unified Celebrity Theory.

The 2006 equation correctly predicted doom for Demi Moore and Ashton Kutcher; Pamela Anderson and Kid Rock; and Britney Spears and Kevin Federline. It also forecast that Will Smith and Jada Pinkett would probably not make it to their 15th anniversary, in December 2012; so far, they’re still married, but gossip columns are rife with reports of a pending split.

On a happier note, the 2006 equation identified two couples with a good chance to make it to their fifth anniversary, in 2010: Ben Affleck and Jennifer Garner, and Matt Damon and Luciana Barroso. Sure enough, they made it (and are still married).

While the 2006 equation did a good job over all of identifying which couples were most likely to divorce, some of the specific predictions proved too pessimistic. Because Demi was so famous — and much more famous than Ashton — we gave their marriage little chance of surviving a year, but they didn’t split until 2011. We were similarly bearish on Tom Cruise and Katie Holmes (because of his fame, his two failed marriages and their age gap), but they’re still together.

What went right with them — and wrong with our equation? Garth, a self-professed über-geek, has crunched the numbers and discovered a better way to gauge the toxic effects of celebrity. Whereas the old equation measured fame by counting the millions of Google hits, the new equation uses a ratio of two other measures: the number of mentions in The Times divided by mentions in The National Enquirer.

“This is a major improvement in the equation,” Garth says. “It turns out that overall fame doesn’t matter as much as the flavor of the fame. It’s tabloid fame that dooms you. Sure, Katie Holmes had about 160 Enquirer hits, but she had more than twice as many NYT hits. A high NYT/ENQ ratio also explains why Chelsea Clinton and Kate Middleton have better chances than the Kardashian sisters.”

Garth’s new analysis shows that it’s the wife’s fame that really matters. While the husband’s NYT/ENQ ratio is mildly predictive, the effect is so much weaker than the wife’s that it’s not included in the new equation. Nor are some variables from the old equation, like the number of previous marriages and the age gap between husband and wife.

In the fine tradition of Occam’s razor, the new equation has fewer variables than the old one. Besides the wife’s tabloid fame, the crucial ones are the spouses’ combined age (younger couples divorce sooner), the length of the courtship (quicker to wed, quicker to split), and the sex-symbol factor (defined formally as the number of Google hits showing the wife “in clothing designed to elicit libidinous intent”).

But the former explanation seems more plausible to the experts I consulted, like John G. Holmes, a psychologist at the University of Waterloo in Ontario who studies relationships. “Women initiate 70 percent of breakups, so perhaps that’s why their personality and image are more predictive,” he says.

“Research has documented that women who wear skimpy or sexually provocative clothing tend to be higher on the trait of narcissism,” says Dr. Buss, a psychologist at the University of Texas. “My research on married couples found that the trait of narcissism predicted likelihood of sexual infidelity. Those high on narcissism feel entitled to have sex with others. Also, they oscillate between feelings of grandiosity and worthlessness, and the sexual attention helps keep them in the self-aggrandizing region of self-esteem.”

Sexual infidelity is also an excellent strategy for a narcissistic celebrity to get attention from the tabloids. And while the tabloids are happy to go after cheaters of either sex, Dr. Buss says that that research into marriage longevity shows there’s still a double standard: “Sexual infidelity by women is statistically more likely to lead to marital breakup than sexual infidelity by men.”

Of course, correlation doesn’t mean causation, says Betsey Stevenson, an economist at Penn who has studied marital longevity. “We know that people marrying young have a much higher chance of divorcing,” Dr. Stevenson says. “But what’s much harder to tell is whether the types of people who marry young are more likely to divorce, or whether the young age at time of marriage actually makes the marriage more prone to divorce.”

Either way, we can still use these variables to make predictions. (For a full list, go to nytimes.com/science.) The good news is that, aided by long courtships, a few couples have a better-than-even chance of lasting at least 15 years: Kate and Prince William, Calista Flockhart and Harrison Ford, Chelsea Clinton and Marc Mezvinsky, and Beyoncé Knowles and Jay-Z.

Many others are likely to split between their 5th and 15th anniversaries (including Tom and Katie, now in their sixth year), and some aren’t likely to make it that long. After he crunched the numbers, Garth’s advice to Jessica Simpson and Ms. Spears is to avoid marriage anytime soon. And he doesn’t hold out much long-term hope for a Kardashian sister married to a pro basketball luminary.

“I’ve calculated the chance of Khloe Kardashian and Lamar Odom celebrating their golden anniversary,” he says, “Even when I extend it to 15 decimal places, the probability is still zero.”

A version of this article appears in print on March 13, 2012, on Page D3 of the New York edition with the headline: Refining the Formula That Predicts Celebrity Marriages’ Doom. Order Reprints|Today's Paper|Subscribe